"""
演示如何回收内存中的实例
"""


class Point:
   def __init( self, x=0, y=0):
      self.x = x
      self.y = y
   def __del__(self):
      class_name = self.__class__.__name__
      print(class_name, "destroyed")

pt1 = Point()
pt2 = pt1
pt3 = pt1
print(id(pt1), id(pt2), id(pt3)) # prints the ids of the obejcts
del pt1
del pt2
del pt3